The invention relates to a digital demodulator on a semiconductor base in which the input for the signal to be demodulated is connected to at least two consecutive pulse-controlled bistable flip-flops.
Such a demodulator is described in the publication "Elektronik", 1975, Vol. 10, p. 104/105, incorporated herein by reference. A decade counter with decoded outputs is provided in this demodulator, said counter being available in the form of an integrated semiconductor module (CD 4017 AE). The input for the signal to be demodulated is connected to the reset input 15 of this module via the parallel circuit of a diode having an ohmic resistance--which forms the actual demodulator--said module being simultaneously connected to ground via a capacitance. The pulse for the operation of the module is simultaneously supplied by the input of the signal to be demodulated and is connected at its input referenced 14. The decoded and demodulated impulses appear at the outputs of the module.
Such demodulators characterized by an externally series-connected diode and RC combinations, however, have the following disadvantages:
(a) they cannot be completely integrated into MOS circuits; PA1 (b) they lead to time-dependent discharge and charge curves which is due to the time constant of the external RC element; PA1 (c) they lead to distortions of the demodulated signal on the basis of the discharge time constant; PA1 (d) a strong influence upon the threshold values takes place by means of the preamplifier when weak input signals are present; PA1 (e) signal breakdowns can mutilate the code; and PA1 (f) the dimensioning of the derivative capacitance and of the ohmic resistance of the known demodulators is necessarily a compromise between the integration time constant, which is to be large in view of malfunctions, and the discharge time which is to be small for small impulse distortions.